1. Field of the Invention
The present invention relates to a power supply system having two charge systems and, more particularly, to a power supply system that can continue to supply an electric power to an electric load or a power source apparatus of vehicles even on the occasion of occurrence of any fault in components.
2. Description of the Related Arts
In hybrid cars or idling stop cars, as compared with conventional engine cars, it is necessary to charge a more electric power. Therefore, an arrangement has been proposed, and in which a generator is made to be of high output, a generated power thereof is charged in a high-voltage battery, and an electric power having been generated by this high-output generator is fed to an electric load in a low-voltage system of vehicles via a DC converter.
However, in such an arrangement in which high-voltage system and low-voltage system are connected together via a DC converter, in the case of occurrence of any fault in the DC converter, not only power feed to an electric load in the low-voltage system cannot continue, but also the breakdown of an electric load in the low-voltage system may be induced. Therefore, several attempts related to measures against the fault of the DC converter have been conventionally proposed. For example, a method has been proposed, and in which in the case of occurrence of a short circuit fault at the DC converter, by stopping the power generation of a generator or by reducing the amount of power generation, an electric load or a power source apparatus in the low-voltage system is protected. (For example, refer to the Japanese Patent Publication (unexamined) No. 218646/2002).
In the above-mentioned Japanese Patent Publication (unexamined) No. 218646/2002, however, only measures in the case of occurrence of a short circuit fault at the DC converter is proposed, but a fault mode of the DC converter is not limited to this one. For example, due to any fault in an internal part of the DC converter, there is a mode in which an output comes to over-voltage or a mode in which an output comes to over-current. In the case of occurrence of these fault modes at the DC converter, since an electric power of not less than a rating is applied to an electric load or a power source apparatus in the low-voltage system, this case likely to result in the deteriorated performance due to over load or, at worst, their destruction.
Furthermore, other than the faults of the DC converter, for example, measures in the case of occurrence of any error in components forming a high-voltage power source system are needed in order to protect an electric load or a power source apparatus as well. For example, in the case of occurrence of a short circuit fault at the power source apparatus, there is a possibility that the power sources system of vehicles is brought in a short circuit thereby causing inoperative of the electric load. In the above-mentioned Japanese Patent Publication (unexamined) No. 218646/2002, there is no description at all as to the fault modes against which measures have to be made other than faults at the DC converter. In addition, the Japanese Patent Publication (unexamined) No. 218646/2002 proposes an attempt of reduction of the amount of power generated at a generator in the case of occurrence of the short circuit fault at the DC converter. However, in the case that the amount of power generation is reduced to a voltage value lower than the voltage in the low-voltage system, since an electric power cannot be fed via the DC converter, the foregoing proposal cannot be said effective.